FIG. 1 shows a portion of a prior art reverse flow annular combustion chamber designated by reference numeral-conventional downstream wall 4 is comprised of a shroud 5 disposed about a liner 6 which is referred to as the outer transition liner. The liner 6 is attached to a combustor wall 8 which has a plurality of holes for injection cooling air for dilution mixing with the hot combustion gas. Dilution mixing of this cool air with the hot combustion gas immediately downstream of the flame zone is well known in the art. The dilution air is used to properly mix the hot gas, thus eliminating hot spots or streaks in the gas flow and assuring a uniform temperature profile. During combustion, the liner 6 is exposed to the hot gas exiting the combustion chamber and therefore requires cooling. This cooling is provided by a portion of the high momentum air exiting the compressor 7, represented by arrows 9, which flows through the cooling passages 3 in a radially inward, (i.e. towards the engine centerline) direction exiting as low momentum air at the inner portion of the liner 6 and is then dumped into the gas stream upstream of the first stage turbine stator, not shown.
As gas turbine engine technology advances, these engines are required to operate at higher pressure ratios and higher combustor exit temperatures. To attain these higher temperatures requires high fuel/air ratios in the combustor. As a result, these combustors use up most of the air exiting the compressor in the combustion process, leaving only a small amount of air, if any, for cooling the outer transition liner of the combustor and for dilution mixing with the combustion hot gas.
Accordingly, there is a need for a combustor in which the air used for cooling the outer transition liner is also used for dilution mixing.